In terms of the simplest cut-off function, the sealing function of the valve in the machinery is to prevent the medium from leaking out or blocking the external substances from entering the interior along the joint between the parts in the cavity where the valve is located. The collar and components that play the role of sealing are called seals or sealing structures, which are called seals for short. The surfaces that contact with the seals and play the role of sealing are called sealing surfaces.

The sealing surface of the valve is the core part of the valve, and its leakage forms can be generally divided into these types, namely, the leakage of the sealing surface, the leakage of the sealing ring connection, the leakage of the sealing part falling off and the leakage of the foreign matters embedded between the sealing surfaces. One of the most widely used valves in pipeline and equipment is to cut off the flow of medium. Therefore, its tightness is the main factor to determine whether internal leakage occurs. The valve sealing surface is generally composed of a pair of sealing pairs, one on the valve body and the other on the valve disc